DE-OS 29 32 287 proposes a vibration pile driver for ramming and/or pulling of rammed bodies such as posts and piles, etc., with the drivers having at least two synchronous eccentric rotors each of which can be driven by at least one motor and one gear box, and each of which has at least two eccentric masses which can be driven around the same axis and adjusted angularly relative to each other, whereby the eccentric masses of each eccentric rotor are mounted on separate shafts arranged concentrically to each other, and whereby, for at least one of these shafts, an adjustment device is provided for displacing the phase position of one shaft relative to the other shaft. The phase adjustment device is integrated in part into the gear box. One of the shafts of the eccentric rotors takes the form of a hollow shaft supported on the other. The phase adjustment device is a part of a planetary gear system whose planet wheel, engaging an annular gear forming the sun wheel of the shaft to be rotated, forms the drive wheel of this shaft, whereby this shaft is adjustable relative to the other shaft along a circle concentric to the latter, in order to adjust the phase position. The planet wheel can be driven via a bypass gear, by a transmission gear which, at the same time serves to drive the other shaft of the eccentric rotors. The vibration pile drive is constructed in such a way that the gears engaging the planet wheel are supported at least partially by a bearing arranged between and connected to two swivel mounted levers. One swivel mounted lever can be swung around the axis of the two shafts of the one eccentric rotor which is adjustable relative to each other. The other swivel mounted lever can be swung around the axis parallel to the axis of the transmission drive shaft. The swivel action of one of the swivel mounted levers is continuously adjusted between two end positions. The planet wheel and the intermediate gear wheel of the bypass gear are each connected in bearings to one of the two swivel mounted levers. In the bearing assembly, these two gears are engaged by two intermediate gears arranged between them. The bearing positions of all of the gears define the corners of a trapezium. A cylinder and piston acts as an adjustment device, the piston rod of which is connected to a swivel mounted lever. The maximum arc described by the swivel mounted lever corresponds to a rotation of the rotor shaft through 180.degree. relative to each other. The vibration pile driver is equipped with an indicator device showing the effective static moment thereby permitting the static moment of the vibration pile driver to be remotely controlled and continuously adjusted from zero to a maximum value during a ramming or pulling action.
The prior art device is extraordinarily complicated in construction. This may be the reason why it has, to date, not been possible for this design to be used in practice.
With the vibration pile drivers used in practice, there is a risk of resonance if the operating speed drops, so that uncontrollable vibrations can be transmitted to nearby buildings and in the ground across a wide area of, for example, 50 to 200 meters. In order to make resonance-free vibration work possible, a high reserve of performance must always be provided so that a strong centrifugal force and a constant operating speed is always available even with the heavy ram material and in heavy soil conditions. This is very important when working in residential areas, near railway installations and other buildings sensitive to vibration.
A further cause of resonance vibrations from hydraulic vibration pile drivers is the long start-up and breaking times of the eccentric masses. This enormous disadvantage has its origins in the physics and of the design of the equipment and can only be eliminated conditionally at the expense of rapid wear of the hydraulic drive motors. When the vibration driver is started up, the aperiodic vibration must be generated immediately at full power. This means high operating pressure and long run-up to the nominal speed of the eccentric masses. As a rule, a resonance range is run through linearly relatively slowly, with the result that, during this period, resonance vibrations can build up and affect the ground for a relatively long time. The same effect occurs during deceleration of the eccentric masses, when the resonance range runs through the time determined by the design. The result of reducing the start-up and braking time is that the inertia of the rotating masses (eccentrics, shafts, couplings) could cavitate the hydraulic motors which would fail after a short time.
DE-PS 35 15 690 proposes a vibration pile drive with eccentric adjustment for ramming and/or pulling ram material, with at least two eccentric motors supported in parallel bearings, and driven by at least one motor and gear box synchronously and oppositely. Each of these eccentric motors comprises two eccentric masses mounted on concentrically arranged shafts synchronously driven and adjustable angularly relative to each other by an adjustment device. Each of the first eccentric masses of both eccentric motors can be driven in opposite directions via a first gear train and each of the second eccentric masses can be driven in opposite directions by a second gear train. The eccentric motor is constructed in the form of a rotary piston adjustment device, in which both eccentric masses are arranged in a cylindrical closed housing and the first eccentric mass forms a radial web permanently attached to the housing, while the second eccentric mass forms the radial blade which can be rotated within limits in the housing and is sealed off from the housing and the web. Hydraulic fluid is applied to each of the two chambers formed between the blade and the web, alternately through their own control conduit. Essentially each eccentric mass is, in cross section sectored, with each eccentric mass extending through a quarter circle. The eccentric mass forming the blades is connected with an internal shaft, in which axial holes are provided for the hydraulic fluid, whereby the control conduits are connected to the ends of the shaft and are sealed off from the shaft by shaft seals. The design of the second eccentric rotor is similar to that of the first eccentric rotor, except for the fact that, with the second eccentric rotor, the two chambers are connected to each other by a connection hole and two control conduits are eliminated. The hydraulic motors grip the shafts of the second eccentric rotor. The angle of the eccentric masses can be adjusted relative to the eccentric rotors both during operation and when stationary. This is achieved, for example, by introducing hydraulic fluid into chambers via a valve and control conduits, while, at the same time, hydraulic fluid emerges from another chamber via a control line. The closer the two eccentric masses approach each other, the greater the static moment, which reaches its maximum when the approach of the two eccentric masses is complete. Conversely, the two sectored eccentric masses can be adjusted in opposite directions by the corresponding introduction of hydraulic fluid. If they are arranged diametrically opposite to each other, the centrifugal force of the eccentric masses cancel each other out, and a minimum static moment is achieved. Between these two extreme positions, any intermediate position is possible via a valve, both during operation and while the vibration pile driver is stationary. This opens the possibility of running up these vibration pile drivers without an activated eccentric mass through the critical range and of switching in or activating the eccentric mass or the eccentric masses once the critical speed range (resonance range) has been passed and, when reducing the speed, of again switching out or neutralizing the eccentric masses above the critical resonance range. The disadvantage with this prior art construction is that the relatively complicated construction requires forced synchronization of the eccentric actuators through a reducing gear.
DE-OS 41 39 798 proposes a vibration pile drive in which each eccentric shaft has a hollow rotating piston which is provided with an adjustable eccentric mass. The longitudinal axis of each piston is arranged orthogonally to the longitudinal rotational axis of the corresponding eccentric shaft. Each of the pistons takes the form of a cylinder in which the corresponding cylindrical eccentric mass is arranged so as to the axially displaceable. Pressure transmitting conduits are connected to the cylinders through which pressure media can be applied to cylinder compartments working in the same direction, by partial flow currents, whose basic parameters (flow pressure, flow volume and flow speed) are equally dimensioned. These vibration pile drivers are aimed at achieving a relatively simply construction with which nevertheless the static moment required at each point can be achieved in order to avoid damaging resonance vibrations. In addition, the aim is to be able to adapt to existing operating conditions are required.
At the start of a ramming operation, for example, light ramming work, or at the end of a pulling operation, the static moment is reduced, i.e. reduced centrifugal force at a constant speed, whereby it is perfectly possible to set the centrifugal force to zero. This results in considerably less vibration. Adaptation to the progress of the ramming operation is easily possible by adjusting the eccentric forces.
For heavy ramming operations, if power requirements become so large that the speed drops, the speed can be maintained by reducing the static moment so that disturbing vibrations in the ground and the surrounding area can be avoided. This is very important, for example, when working in residential areas, near to railway installations and other vibration sensitive buildings. Under certain circumstances, the fall off of speed on vibrators with no static moment or centrifugal force adjustment facility during operation, ground vibration can become so great that ramming or pulling operations can no longer be carried out without the risk of building cracking or being similarly damaged.
During the raising and lowering of vibration pile drivers, the eccentric masses are practically switched out, i.e. they are no longer effective as eccentric masses. This means that considerably lower resonance force is applied to the boom, which resonance forces could otherwise prematurely destroy the boom. By this means, efficient operations is achieved which includes a saving in energy. Operationally unfavorable combinations of speed and static moments are therefore avoidable.
As the eccentric masses are attached to the agitator shafts, special bearings, machine parts, gears and complicated planet gears no longer need to be used. This results in a significantly more simple design and a compact and relatively light construction. As a consequence, the entire vibration ram applies only relatively little load to the ram material, avoiding the tendency to buckle and the center of gravity can be favorably located.
The agitator shafts are fashioned as hollow bodies whereby, in each of the hollow shafts, there is at least one piston axially displaceable within the hollow shaft. The corresponding cylindrical compartments in the hollow shafts are each connected to the same pressure media conduit so that the pistons can be adjusted synchronously and in the same direction by pressure medium pressure whose basic parameters (flow pressure, flow volume and flow speed) are equal. For example, pistons representing the eccentric masses can be loaded in their neutral position (zero position) by pressure from a pressure medium, in particular, hydraulic pressure. By correspondingly removing the pressure medium pressure, the pistons can be adjusted continuously to the particular position required by the centrifugal force of the rotating hollow shafts, whereby the eccentric masses are continuously adjustable from their neutral position to their maximum position. By this means, any rotational speed or any particular position can be related to the eccentric masses thus making corresponding adjustments of the static moments possible.
In the zero position (neutral position), the pistons can be located on, or almost on, the rotational axis of the agitator, so that no, or only a minimal, eccentric force and thus no centrifugal force, can develop. As soon as the pistons move away from a neutral position, a specific static moment, depending upon the position of the piston, and a specific centrifugal force depending upon the speed develop. When the piston reaches its end position, the maximum static moment and maximum centrifugal force are reached.
The adjustment can actually be effected hydraulically, pneumatically or electro-mechanically. However, in practice, hydraulic adjustment will probably be given preference.